Can we say any riflescope is truly optically perfect? No, but in practice a riflescope can be considered to be perfect for its intended use when there are no perceivable residual aberrations, even under the closest scrutiny from qualified users. This of course means qualified users who know what they're looking at and looking for. When residual aberrations can only be detected using precision instruments and are impossible to see with the naked eye, as is the case with this Leica Magnus 1.8-12x50i, we can truly say it’s an excellent product that’s worthy of the Leica name in the optical field, a riflescope that sets the standard in terms of riflescope quality.
In this article, we’ve run a full test on the riflescope, concentrating especially on its optical and mechanical features.
So how do you test a riflescope? There are two severe tests: the lamp test and the practical test at the firing range. The first is done at night using a street lamp with the zoom adjusted so the lamp fills the field of view. If there is any trace of reflections down the tube, this will show up during the test. Personally I think street lamps are an even harsher way to test a riflescope for ‘flare’ than using a Siemens star. The other test is done with the riflescope and a target at a firing range. The riflescope must be adjusted to its max. magnification. An air rifle target is placed at a range of 200 metres, the riflescope is mounted in a stable way on a very heavy support, which if possible is also weighed down with sandbags, then you take careful aim at the target. Without moving the instrument, you adjust it 15 clicks up, 15 to the right, 15 down and 15 to the left; after this the riflescope must be on the exact same spot on the target as before, which is exactly what happens with the Leica riflescope.
The turrets can be adjusted by hand, without the need for any tools; you can loosen the screw at the centre of each turret using a coin to reset the calibration to zero without the need to do complicated calculations or refer to notes. The riflescope’s magnification adjustment ring features a practical cam that makes it easier to use.
At this point there’s also another test to perform, which we wouldn’t do on a lesser riflescope, as riflescope mechanisms are usually precise but delicate too. In this test each turret is turned quickly to the right by around twenty clicks, then turned twice as much the opposite way, and finally back to its original position. We repeated the test, and as hard as we tried never managed to budge the riflescope from its initial position.
The reticle on the second focal plane can be lit in day or night mode, indicated by the sun and moon symbol; the central position indicates that the reticle is off.
A 60-step control on the top of the battery compartment is used to fine-tune the brightness. This brightness setting is saved and the riflescope will still be set up at just the same brightness next time you use it. The outer surfaces of the lenses are treated with a special coating that Leica calls AquaDura, which makes water slide off the lens without leaving marks or beading on the surface. This is extremely useful, as when hunting you’re out in the open and there’s always the chance it’ll rain. What’s more, thanks to the 50 millimetre front lens, even on rainy days you’ll always have enough light coming into the riflescope.
So let’s have a look at the optics.
Light transmission is over 91%, which is a figure very few riflescopes can match. Considering the fact that a lens has two glass surfaces in contact with the air, each of which produces reflections that reduce optical quality, to obtain light transmission figures of over 91% in a normal 9-lens zoom layout, each lens has to transmit 99.5%, a result which is of course very close to theoretical perfection and corresponds to what is feasible in practice. At four magnification settings, on a night lit by a full moon, you can see everything.
There is so little coma effect when using the riflescope to observe a star that it’s almost non-existent. The same can be said for astigmatism, checked by observing an antenna pylon with both horizontal and vertical lines.
Spherical aberration is of course compensated for by the fact that the human retina isn’t flat. You won’t see any vignetting in this riflescope. There’s no curvature of field, which would make it impossible to have the same clear image in the centre and at the edges of your field of view. We checked the distortion, or rather the absence of it, by observing the iron bars of a window that met at a right angle so the image filled the field of view completely. There was no barrel or pincushion distortion.
So have we found the perfect riflescope? No, because there’s no such thing as perfection in the field of optics. For ever increasing prices you can find even better optical aberration correction, but we’re talking about quite minor differences to be found only in scientific instruments, and there’s no such thing as total correction.